The present invention relates to amorphous metallic alloys and their manufacture.
Amorphous metallic alloys are known which have essentially no crystalline microstructure when rapidly cooled to a temperature below the alloy glass transition temperature before appreciable grain nucleation and growth occurs. For example, U.S. Pat. No. 5,735,975 discloses amorphous metallic alloys represented by the alloy composition, (Zr,Hf)a(Al,Zn)b(Ti,Nb)c(Cux,Fey(Ni,Co)z)d that can be rapidly solidified to produce an amorphous body. The patent indicates that an appreciable amount of oxygen may dissolve in the metallic glass without significantly shifting the crystallization curve. However, the amorphous metallic alloys described in above U.S. Pat. No. 5,735,975 typically are made from pure, laboratory grade components and have a low bulk oxygen impurity content of less than about 200 ppm by weight (or 800 ppm oxygen on an atomic basis).
The present invention arose from attempts to make amorphous alloys described in the above U.S. Pat. No. 5,735,975 using commercially available raw materials and conventional vacuum die casting equipment. The inventor discovered that bulk oxygen impurity concentrations achievable in the alloy using commercially available raw materials and conventional vacuum melting/die casting equipment were well above the low bulk oxygen impurity concentration of 200 ppm by weight oxygen (800 ppm oxygen on atomic basis) typically present in the patented alloys. The inventor also discovered that such amorphous alloys having a relatively high bulk oxygen impurity concentration could be conventionally vacuum die cast in a plate specimen configuration up to a plate cross-sectional thickness of only 0.1 inch while retaining a bulk (substantially 100%) amorphous microstructure.
An embodiment of the present invention involves an amorphous alloy of the type set forth in the ""975 patent made from commercially available raw materials that can be conventionally cast to a substantially greater thickness while retaining a bulk amorphous microstructure. The invention involves providing an intentional addition of yttrium (Y) in the alloy that exceeds zero yet does not exceed about 0.5 atomic % based on the alloy composition, and preferably is in the range of about 0.2 to about 0.4 atomic % Y based on the alloy composition. The Y addition to such amorphous alloys having a relatively high bulk oxygen impurity concentration after the alloy is melted and cast increases alloy resistance to crystallization such that bulk amorphous products with greater dimensions can be made using commercially available raw materials and conventional casting processes.
In an illustrative embodiment of the invention, a Zr based amorphous alloy is provided having an alloy composition, in atomic %, consisting essentially of about 54 to about 57% Zr, about 2 to about 4% Ti, about 2 to about 4% Nb, about 8 to about 12% Al, about 14 to about 18% Cu, and about 12 to about 15% Ni, and about 0.2 to about 0.4% Y with an alloy bulk oxygen impurity concentration of at least about 1000 ppm on an atomic basis. Such an amorphous alloy can be conventionally vacuum melted and die cast to form a bulk amorphous cast plate having a cross-sectional thickness up to 0.2 inch, which is twice the thickness achievable without Y being present in the alloy, despite having relatively high bulk oxygen concentration after melting and casting.
The above and other advantages of the present invention will become more readily apparent from the following drawings taken in conjunction with the following detailed description.